1. Field of the Invention
This invention relates to a photosensitive member for electrophotography, and more particularly to a photosensitive member for electrophotography of negative charge type which is useful as a photoreceptor of duplicator.
2. Description of the Related Art
In recent years, a photosensitive member for electrophotography made of an a-Si (amorphous silicon) having excellent properties of high photoconductivity and high hardness and being non-pollutive has been given special notices. The a-Si photosensitive member is generally fabricated; by plasma CVD process in such manner that a source gas such as monosilane (SiH4) or disilane (Si.sub.2 H.sub.6) is introduced into a vacuum chamber and applied with a radio frequency (rf) power to form a glow discharge, so that the source gas is decomposed to deposit a photoconductive layer mainly of a-Si on a substrate; or by reactive sputtering process in such manner that a silicon wafer is used in place of the above source gas as a target for sputtering and H.sub.2, He, Ar or like gas is introduced and applied with a rf power to form a glow discharge so as to sputter the target Si wafer, thereby depositing a photoconductive layer mainly of a-Si on the substrate.
The a-Si photoconductive layer fabricated above usually contains hydrogen of 10 to 30 at. % and exhibits a slightly n-type conduction even when not added, i.e., non-doped, with a conductivity-controlling impurity (for example, B (boron) of III group element, P (phosphorus) of V group element and the like). Since the electron as a carrier is superior in mobility than the hole, the a-Si photoconductive layer inherently exhibits a high photoconductivity but shows a relatively high dark conductivity such as 10.sup.-9 to 10.sup.-10 S/cm. The photoconductive layer having such conductivities, when applied as it is to a photosensitive member for electrophotography of negative charge type, is inferior in charge acceptance and dark decay characteristic (charge retentivity) due to the relatively high dark conductivity.
In this regard, there have been proposals in the production of a photosensitive member for electrophotography of negative charge type:
(1) Adding a chemical modifier such as C, N, O or the like in the a-Si photoconductive layer of the member to lower the dark conductivity, or
(2) Constituting the photoconductive layer of the member with a carrier-generation layer made of a non-doped a-Si and a carrier-transportation layer made of an a-Si added with the chemical modifier C, N, O or the like.
These proposals, however, have a drawback that although the dark conductivity of the photoconductive layer constituting the photosensitive member is lowered, the photoconductivity thereof is also lowered as the dark conductivity lowers. Further, according to these proposals, a n-type high photoconductivity which is the characteristic of the non-doped a-Si is not utilized nor developed while necessitating the addition of the chemical modifier and the cumbersome control of addition amount thereof.
In the meantime, it has been known that an a-Si layer can be fabricated by ECR process (electron cyclotron resonance process) (U.S. Pat. No. 4,532,199). Also, we have proposed that an a-SiGe layer, an a-Si/a-SiGe composite layer or an a-SiX layer (wherein X represents C, N or O) each fabricated by ECR process can suitably be applied as a photoconductive layer of photosensitive member for electrophotography mainly of positive charge type (US patent application Ser. Nos. 368,807, 372,019 and 369,473). However, it is still not known of fabricating by ECR process an a-Si photoconductive layer in the photosensitive member for electrophotography of negative charge type.